All 46 runbook_url annotations pointed at https://<apex>/runbooks/<name> and every one returned 404 — there was no runbooks/ directory and no route. Every alert that reached a human handed them a dead link at the moment they needed it. Runbooks are now served from their own non-gating tier at the apex prefix, PUBLIC on purpose: gating them behind Keycloak would make keycloak-down unreadable exactly when Keycloak is down, which is a loop with no exit. The new L0 guard checks both directions — a runbook_url with no file, and a file not wired into the generator — and it caught a live one on contact with main: CNPGPrimariesCoLocated had shipped hours earlier pointing at a runbook that did not exist.